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Discoveries of water on Mars are now so common that the subject has become the butt of jokes among planetary scientists: “Congratulations—you've discovered water on Mars for the 1,000th time!”

Most of these findings have involved either visual evidence for ancient, long-gone water or evidence for present-day ice, vapor or hydrated minerals. The discovery of actual liquid water on the surface, in the present day, could change the course of Mars exploration. Where there is water on Earth, there is almost always life. Confirming the existence of water on Mars would therefore greatly improve the prospect of finding extraterrestrial life. This is the story of continuing efforts to uncover what role, if any, liquid water plays on Mars today.